首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   31164篇
  免费   4305篇
  国内免费   3452篇
化学   16935篇
晶体学   296篇
力学   1439篇
综合类   239篇
数学   2659篇
物理学   9141篇
无线电   8212篇
  2024年   108篇
  2023年   748篇
  2022年   909篇
  2021年   1159篇
  2020年   1190篇
  2019年   1098篇
  2018年   873篇
  2017年   898篇
  2016年   1279篇
  2015年   1287篇
  2014年   1594篇
  2013年   2051篇
  2012年   2519篇
  2011年   2431篇
  2010年   1734篇
  2009年   1741篇
  2008年   2001篇
  2007年   1876篇
  2006年   1802篇
  2005年   1509篇
  2004年   1152篇
  2003年   989篇
  2002年   868篇
  2001年   689篇
  2000年   713篇
  1999年   809篇
  1998年   687篇
  1997年   584篇
  1996年   589篇
  1995年   507篇
  1994年   459篇
  1993年   394篇
  1992年   338篇
  1991年   289篇
  1990年   272篇
  1989年   178篇
  1988年   137篇
  1987年   102篇
  1986年   109篇
  1985年   83篇
  1984年   40篇
  1983年   42篇
  1982年   40篇
  1981年   23篇
  1980年   9篇
  1979年   7篇
  1976年   1篇
  1957年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
多信道E1映射复用成帧芯片PM8316及其应用   总被引:1,自引:0,他引:1  
PM8316是PMC-Sierra公司生产的一种低功耗、高性能的多信道E1映射复用成帧芯片。该芯片内部集成了映射器、复用器、成帧器,其处理容量为63路E1,并含有8位微处理器总线接口和5个标准信号的JTAG测试端口,可支持收发抖动衰减。文中介绍了PM8316的主要功能和接口,给出了它在SDH终端设备中的主要信号电路框图。  相似文献   
82.
There exist a number of typical and interesting systems and/or models, which possess three-generator Lie-algebraic structure, in atomic physics, quantum optics, nuclear physics and laser physics. The well-known fact that all simple 3-generator algebras are either isomorphic to the algebra sl (2, C) or to one of its real forms enables us to treat these time-dependent quantum systems in a unified way. By making use of both the Lewis-Riesenfeld invariant theory and the invariant-related unitary transformation formulation, the present paper obtains exact solutions of the time-dependent Schr?dinger equations governing various three-generator Lie-algebraic quantum systems. For some quantum systems whose time-dependent Hamiltonians have no quasialgebraic structures, it is shown that the exact solutions can also be obtained by working in a sub-Hilbert-space corresponding to a particular eigenvalue of the conserved generator (i.e., the time-independent invariant that commutes with the time-dependent Hamiltonian). The topological property of geometric phase factors and its adiabatic limit in time-dependent systems is briefly discussed. Received 6 July 2002 / Received in final form 21 October 2002 Published online 11 February 2003  相似文献   
83.
In this letter, we report a novel microstrip interdigital hairpin resonator by having the parallel coupled lines in a conventional miniaturized hairpin resonator replaced by an interdigital capacitor. Equations are derived in order to design the resonator with an optimal physical length. It will be proved that the novel resonator can achieve even more size reduction than the conventional miniaturized hairpin resonator owing to the employment of the slow-wave structure. Finally, a four-pole cross-coupled bandpass filter using the optimal resonator is fabricated as verification  相似文献   
84.
In multiprocessor-based system-on-chips (SOCs), optimizing the communication architecture is often as important as, if not more than, optimizing the computation architecture. While there are mature platforms and techniques for the modeling and evaluation of computation architectures, the same is not true for the communication architectures. A major challenge in modeling the communication architecture is managing the concurrency at multiple levels: at the operation level, multiple communication operations may be active at any time; at the microarchitecture level, several microarchitectural components may be operating in parallel. Further, it is important to be able to clearly specify how the operation-level concurrency maps to the microarchitectural-level concurrency. This paper presents a modeling methodology and a retargetable simulation framework which fill this gap. This framework seeks to facilitate the design space exploration of the communication subsystem through a rigorous modeling approach based on a formal concurrency model, the operation state machine (OSM). Our OSM-based modeling methodology enables the entire system including both the computation and communication architectures to be modeled in a single OSM framework. This allows us to develop a tool set that can synthesize cycle-accurate system simulators for multiprocessing-element SOC prototypes. We show that, by simulation, critical system information such as timing and communication patterns can be obtained and evaluated. Consequently, system-level design choices regarding the communication architecture can be made with high confidence in early stages of design.  相似文献   
85.
浅谈集成电路的废气处理   总被引:1,自引:1,他引:0  
集成电路的工业废气有含氟化物、硫酸雾的酸性废气,含氨的碱性废气,含异丙醇、光刻胶的有机废气,含SiO_2的含尘废气,以及含硅烷、磷烷的工艺尾气等,这些工业废气中大部分成分是有毒有害的,必须进行有效的处理才能排入大气中。主要讨论上述工业废气的分类、处理方式、应用范围及应用实例等。  相似文献   
86.
高职物理教学中涉及到合成与分解的地方主要有两处:一是力的合成与分解,另一是运动的合成与分解。由于学生在初中物理和数学教学中从未学过矢量概念,而高职数学中矢量的教学又要到很迟才进行,学生学习“合成与分解”的困难很多,笔者从以下几方面进行尝试,以解决学生在学习中的难点,消除模糊认识。  相似文献   
87.
This paper firstly examines the value of optical bypass scheme in packet ring networks. An Integer Linear Program (ILP) formulation is presented and analytical results under different traffic patterns are given.  相似文献   
88.
利用电位差计的高精度,设计出合理的实验电路对C31型电表进行校准,使得电表的准确度等级得以提高。  相似文献   
89.
In many situations such as the cores of a rotating electrical machine and the T joints of a multiphase transformer, the local flux density varies with time in terms of both magnitude and direction, i.e. the flux density vector is rotating. Therefore, the magnetic properties of the core materials under the rotating flux density vector excitation should be properly measured, modeled and applied in the design and analysis of these electromagnetic devices. This paper presents an extensive review on the development of techniques and apparatus for measuring the rotational core losses of soft magnetic materials based on the experiences of various researchers in the last hundred years.  相似文献   
90.
The 3-D modeling of heads by using optical triangulation techniques is of great interest in the context of virtual reality, telecommunication and computer animation. This paper presents a structured light-based system mainly for human heads. It is named “3-D Laser Color Scanner” (3DLCS). A 3-D model is obtained with a cylindrical scan. The laser beam is switched on and off using a “light valve” and two successive CCD frames are captured, one with the laser line showing and one without. We can simplify the laser line extracting by subtracting these two images.In this system, two CCD cameras are used to avoid occlusion problems. Color information is read from the CCD when the laser light is absent. Since traditional laser scanner will miss the range data in the low-reflectance areas such as the hair area of human head, a shape from silhouette algorithm is presented to overcome this problem. Finally, we give some results using our system. The resulting model is suitable for many applications.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号